sustainability Article Evaluating Nature-Based Solution for Flood Reduction in Spercheios River Basin under Current and Future Climate Conditions Christos Spyrou 1,2,* , Michael Loupis 1,3 , Nikos Charizopoulos 4,5 , Ilektra Apostolidou 1, Angeliki Mentzafou 1,6 , George Varlas 6 , Anastasios Papadopoulos 6 , Elias Dimitriou 6 , Depy Panga 1, Lamprini Gkeka 1, Paul Bowyer 7, Susanne Pfeifer 7 , Sisay E. Debele 8 and Prashant Kumar 8 1 Innovative Technologies Centre (ITC), 116 33 Athens, Greece; [email protected] (M.L.); [email protected] (I.A.); [email protected] (A.M.); [email protected] (D.P.); [email protected] (L.G.) 2 National Observatory of Athens, Institute for Astronomy, Astrophysics, Space Applications, and Remote Sensing (IAASARS), Vas. Pavlou & I. Metaxa, 152 36 Athens, Greece 3 General Department, National and Kapodistrian University of Athens, 157 72 Psachna, Greece 4 Laboratory of Mineralogy-Geology, Agricultural University of Athens, Iera Odos 75, 118 55 Athens, Greece; [email protected] 5 Region of Sterea Ellada, Kalivion 2, 351 32 Lamia, Greece 6 Hellenic Centre for Marine Research (HCMR), Institute of Marine Biological Resources and Inland Waters, 190 13 Anavyssos, Greece; [email protected] (G.V.); [email protected] (A.P.); [email protected] (E.D.) 7 Helmholtz-Zentrum Geesthacht, Climate Service Center Germany (GERICS), 20095 Hamburg, Germany; Citation: Spyrou, C.; Loupis, M.; [email protected] (P.B.); [email protected] (S.P.) Charizopoulos, N.; Apostolidou, I.; 8 Global Centre for Clean Air Research (GCARE), Department of Civil and Environmental Engineering, Mentzafou, A.; Varlas, G.; Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK; Papadopoulos, A.; Dimitriou, E.; [email protected] (S.E.D.); [email protected] (P.K.) Panga, D.; Gkeka, L.; et al. Evaluating * Correspondence: [email protected]; Tel.: +30-210-7560322 Nature-Based Solution for Flood Reduction in Spercheios River Basin Abstract: Nature-based solutions (NBS) are being deployed around the world in order to address under Current and Future Climate hydrometeorological hazards, including flooding, droughts, landslides and many others. The term Conditions. Sustainability 2021, 13, refers to techniques inspired, supported and copied from nature, avoiding large constructions and 3885. https://doi.org/10.3390/ other harmful interventions. In this work the development and evaluation of an NBS applied to the su13073885 Spercheios river basin in Central Greece is presented. The river is susceptible to heavy rainfall and Academic Editors: Kuno Kasak, bank overflow, therefore the intervention selected is a natural water retention measure that aims Ülo Mander and Miklas Scholz to moderate the impact of flooding and drought in the area. After the deployment of the NBS, we examine the benefits under current and future climate conditions, using various climate change Received: 19 February 2021 scenarios. Even though the NBS deployed is small compared to the rest of the river, its presence Accepted: 26 March 2021 leads to a decrease in the maximum depth of flooding, maximum velocity and smaller flooded Published: 1 April 2021 areas. Regarding the subsurface/groundwater storage under current and future climate change and weather conditions, the NBS construction seems to favor long-term groundwater recharge. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in Keywords: nature-based solutions; flood; Spercheios; hydrometeorological hazards; climate published maps and institutional affil- iations. 1. Introduction At the highpoint of this era of maximum aggravating human activity and limited Copyright: © 2021 by the authors. ecological awareness, researchers are working on ways to relieve the ecosystems from Licensee MDPI, Basel, Switzerland. pressing climate-related risks. One set of methods, that follow a long-term and site-specific This article is an open access article approach in ecological management, is called nature-based solutions (NBS). The term refers distributed under the terms and to “techniques inspired by, supported by, or copied from nature” [1], which in essence conditions of the Creative Commons means that by applying what we learn from observing nature, we can mitigate hazards Attribution (CC BY) license (https:// in a sustainable manner, avoiding large constructions and other harmful interventions in creativecommons.org/licenses/by/ an effort to address climate change impacts and move towards resilient ecosystems [2]. 4.0/). Sustainability 2021, 13, 3885. https://doi.org/10.3390/su13073885 https://www.mdpi.com/journal/sustainability Sustainability 2021, 13, 3885 2 of 20 Nature-based solutions also foster society-oriented actions and promote broad public participation and transparency enhancement [2–4]. Due to this transdisciplinary, NBS can have a variety of possible positive impacts beyond environmental risk mitigation [5]; their application benefits the society (i.e., by increasing an area’s aesthetical value and enhancing the ecosystem services it provides) and the economy (i.e., energy saving, reducing economic damage; [6]). However, the main goal of NBS deployment remains the mitigation of hydrometeorological hazard impacts on the local population; hazards that are expected to become more frequent and severe due to climate change [7]. In this regard, NBS have nature-based solutions (NBS) have proved to be effective for hydrometeorological risk management [1,8,9]. NBS is a relatively new concept that offers several cost-efficient methods to address such phenomena but also discourages the use of large structural constructions like concrete buildings (green development; [1]). Additionally, the flexibility of NBS allows them to be implemented alone or integrated with other technological or engineering solutions, determined by site-specific natural and cultural contexts [10]. NBS is not the first concept focusing on green solutions that has been officially defined and referred to in academic debates and official legislation. Approaches such as ecosystem- based adaptation (EbA), urban green infrastructure (UGI) and ecosystem services (ESS) have already gained attention [11]. The exact limits of each of the aforementioned concepts are vague, thus it is useful to adopt “NBS” as a broader term connecting and interweaving those individual concepts with one another, giving prominence to their complementar- ity [10,11]. What distinguishes nature-based solutions from other general green approaches is that they are used to address key societal challenges that originate from a combination of natural (climate change and environmental degradation) and anthropogenic (economic and social development and human health) factors [2,10,12]. NBS have recently started to become a key priority to mainstream environmental protection and sustainable use of biodiversity at global and regional scales [12] and frameworks are being developed to enable the assessment of impacts related to specific NBS actions [13]. There are a wide variety of applied solutions, but here we focus on NBS for hydrome- teorological risks: in order to tackle flood risk, for instance, it is crucial to retain water in the landscape by managing overland flow or infiltration [14–16]. A NBS practice is to change the land use from arable to grassland or to create buffer strips using grass and hedges. Similarly, if an increase in floodplain storage capacity is desired, artificial reservoirs or wetlands comprise common green solution techniques [17]. Additionally, several methods have already been implemented in the urban environment, aiming to decrease stormwater generated flooding. These include installations of green rooftops and walls, stormwater gardens and the construction of sustainable drainage systems [16,18]. The process of implementing NBS is rather complex, and there are still major research gaps regarding NBS assessment and implementation. In order to boost such research, the European Commission (EC) is financing several projects. One of the first is OPERANDUM (open-air laboratories for nature based solutions to manage hydrometeo risks), which aims at codesign, codevelopment, deployment and assessment of NBS’s in open-air labora- tories (OAL’s) in ten countries. OAL’s in this project are natural and rural Living Labs that cover a wide range of hazards with different climates, land use and socioeconomic characteristics. Essentially living labs means that interdisciplinary and transdisciplinary research is implemented, strongly related to its territorial context and the societal changes it possibly drives. In this work, we present the development and evaluation of an NBS applied to the Spercheios River Basin in Central Greece. The Spercheios River is generally susceptible to heavy rainfall and river bank overflow due to flood water from upstream, while at the same time deforestation increases its susceptibility to heavy rainfall [19]. Flood events occur regularly exceeding the channel capacity, affecting most elements of the socioeconomic system of the area. The risks, related to flooding in the area, include the potential loss of human life, potential loss of crop production and livestock, damage to properties and infrastructure and difficulties in transportation [20]. Sustainability 2021, 13, x FOR PEER REVIEW 3 of 20 same time deforestation increases its susceptibility to heavy rainfall [19]. Flood events oc- cur regularly exceeding the channel capacity, affecting most elements of the socioeco- nomic system of